Corrosion resistant metallic substrates

ABSTRACT

AN ARTICLE OF MANUFACTURE IS DESCRIBED WHICH COMPRISES A CORROSI ON RESISTANT METALLIC SUBSTRATE. THE NORMALLY CORROSION-PRONE METALLIC SUBSTRATE IS RENDERED CORROSION RESISTANT BY THE APPLICATION OF ABOUT 0.05 TO ABOUT 25 GRAMS OF A HIGH MOLECULAR WEIGHT OLEFIN POLYSULFONE PER SQUARE FOOT OF METALLIC SUBSTRATE. THE SUBSTRATE CAN BE PAINTED BEFORE OR AFTER THE APPLICATION OF THE RESIN. THE RESIN IS APPLIED TO THE SUBSTRATE BY MEANS OF A LIQUID DISPERSION CONTAINING THE DISPERSED RESIN SUCH AS WATER CONTAINING A SURFACTANT OR AN ORGANIC SOLVENT.

United States Patent 015 3,563,789 CORROSION RESISTANT METALLIC SUBSTRATES William Ross Moore, Lake Jackson, Tex., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Feb. 16, 1968, Ser. No. 705,950 Int. Cl. B32b /08 U.S. Cl. 117-75 7 Claims ABSTRACT OF THE DISCLOSURE An article of manufacture is described which comprises a corrosion resistant metallic substrate. The normally corrosion-prone metallic substrate is rendered corrosion resistant by the application of about 0.05 to about 25 grams ofa high molecular weight olefin polysulfone per square foot of metallic substrate. The substrate can be painted before or after the application of the resin. The resin is applied to the substrate by means of a liquid dispersion containing the dispersed resin such as water containing a surfactant or an organic solvent.

This invention relates to new articles of manufacture comprising a normally corrosion-prone metallic substrate coated with a high molecular weight polysulfone resin formed by the copolymerization of sulfur dioxide and an olefinically unsaturated organic compound and a process for rendering the normally corrosion-prone metallic substrates corrosion resistant.

More specifically, this invention relates to coated, normally corrosion-prone metallic substrates which are useful as structural materials such as aluminum, zinc, copper, lead, nickel, iron, magnesium, chromium, tin, and alloys of the above metals with each other and with other metals and coatings of the foregoing on metals.

Examples of such alloys are brass, bronze, Monel, stain less steel, pewter, etc.

While it is well known that iron and steel surfaces require protection to prevent rusting, other structural metals or alloys which are normally thought to be corrosion resistant require protection in certain environments. Thus, tin and its alloys are subjected to severe attack in the presence of strong alkali and the halogens. Aluminum and its alloys are also subject to pitting in the presence of salt water or industrial atmospheres. Even stainless steel is severely corroded in the presence of the chlorides of copper, tin, and mercury.

This invention has for its object the protection of these corrosion-prone metals or alloys by coating them with a high molecular weight polysulfone resin. The resin coated metallic substrates can be subsequently painted over by conventional paints for additional protection or for decorative purposes. Alternatively, the metallic substrates can be first painted, if desired, and then coated with the above olefin sulfone resins. Since the resins are substantially clear and/or colorless, the color of the undercoat is clearly visible. If the metallic luster of the substrate is desired to be displayed the resin coating alone may be used. In either event, a substantial improvement in the corrosion resistance of the metallic substrate is achieved by this invention.

Thus the present invention provides the art with a new undercoat or overcoat for painted metallic substrates as well as a new protective coating when used alone.

Thus, this invention relates to normally corrosion-prone metallic substrates which have been rendered corrosion resistant by a coating of polysulfone resin which is an interpolymer of sulfur dioxide and alpha-olefins of 10-20 carbon atoms.

The polysulfones used in this invention are generally ice well known materials. Their history, preparation and uses are set forth in the article by Fettes and Davis entitled Polysulfones in vol. 13, High Polymers part III, chapter 15, pages 225-270 (1962). This publication is incorporated by reference into this specification. However, only recently has it been discovered how to make high molecular weight olefin polysulfones, which polymers contain more than 50% polymer species above a million molecular weight. This suspension polymerization process which produces the high molecular weight polysulfones used herein is described and claimed in Ser. No. 693,150 filed on Dec. 26, 1967, in the names of B. L. Atkins, W. M. Welch and W. R. Moore and is entitled High Molecular Weight Olefin Polysulfone Resins and Process for their Preparation. This process produces olefin sulfone copolymers which has a peak molecular weight in the general range 1.5)(10 to 2.5x 10 as measured by gel permeation chromatography. This is a well known analytical technique in the polymer field as is illustrated by the article by R. L. Bartosicwicz entitled The Use of Gel Permeation Chromatography As an Analytical Tool in the Coating Industry, Journal of Paint Technology 39:28- 39 #504, January 1967.

It is known in the art to coat various resins, paints, bitumins, rubbers, etc. on metals to protect them from corrosion. See for example Protective Coatings for Metals by Burns et al., American Chemical Society Monograph #163 (1967). However, these coatings suffer from one or more of disadvantages in that they are expensive, require a heavy loading for elfectiveness, instability to heat and light, poor adhesion to paint, odoriferous, or are difiicult to apply.

It has been suggested in U.S. Pat. No. 2,201,544 that olefin polysulfone resins prepared by the use of peroxide type catalysts are useful as coating compositions. However, these resins are disclosed to be insoluble in the common organic solvents and soluble only in acetone.

In contrast to the foregoing, it now has been discovered that olefin polysulfones of a high molecular weight prepared by the process disclosed in the aforementioned application can be applied to the metallic substrates by forming a liquid dispersion containing the resin and either (1) water with a small amount of a surfactant or (2) a volatile organic solvent. Furthermore, it has been discovered that the use of these high molecular weight polysulfone resins gives a coated or treated substrate which is inexpensive, odorless, colorless, and easily prepared.

The resins are dispersed in water by forming a concentrated solution of the resin in a volatile organic solvent such as benzene and adding this to water along with about 1 to 6 percent by weight, based on the organic phase of an emulsifying, or surface active agent, preferably those of the anionic or nonionic type. Examples of nonionic surfactants utilized include alkylpoly (ethylenoxy) ethanols, alkylphenoxypoly(ethyleneoxy) ethanols, alkylpoly(propyleneoxy)ethanols, and alkanol amides, such as those derived from diethanolamine and coconut oil fatty acids. Exemplary of these nonionic surfactants are nonylphenolethylene oxide adducts (Dowfax 9N10). Exemplary of anionic emulsifiers are sodium lauryl sulfate (Duponol WAQE), complex organic phosphate ester (Gafac RE-610), alkylaryl sulfonate (Ultrawet K), and sodium lauryl ether sulfates (Sipon ESY).

The resins are dispersed in volatile organic solvents such as hydrocarbons of 5 to 20 carbon atoms. Examples of these are benzene, n-hexane, diethylbenzenc naphtha, gasoline, kerosene, Stoddard solvent. They can also be dispersed in volatile halogenated solvents of 1 to 10 carbon atoms such as perchloroethylene, methylene chloride, trichlorobenzenes, carbon tetrachloride, 1,1,1-

trichloroethane, chloroform, and fluorocarbons such as l,1,2,2-tetrachlorodifluoroethane and perfiuoro kerosene.

Furthermore, the resins of this invention can be dispersed in volatile oxygenated solvents such as ether, tetrahydrofuran, butyl acetate, p-dioxane, methyl ethyl ketone and dimethyl formamide.

If desired, a mixture of one or more of the above solvents can be used with equivalent results.

4 EXAMPLE 2 In a like manner, aluminum plates (3" x 6" x Reynolds Aluminum Type 6061-T6) were coated with various waxes, including the polysulfone of Example 1, and sealed in a 4.76 percent (weight) NaCl-deionized water static bath for 130 days. The data in Table II was obtained. (Note: These panels were not washed after removal from the test solution.)

TABLE II.CORROSION STUDY OF IOLYSULFONE COATED ALUMINUM IN SALT WATER Initial Wt of Wt. of plate Plate wt.

plate coating alter 130 gain after Condition of plate weight (g./36 days in salt 130 days after 130 days in Coating applied (g.) 111. 1 water (g.) (g.) saltwater Low mol wt. polyethylene wax (Melt Index 80 l) 40. 2501 0.0074 41. 2270 0.8705 Very heavy corrosion. Paraffin wax (M.P. 150 F.) 0.1880 0.0274 40.8607 0.6447 Heavy corrosion. q -C a-olefin polysulfone 39. 9539 0.0155 40. 2173 0. 2479 Very mild corrosion. l .P.(.! 11092723. silicone... 40.2528 0.0238 41.3821 1.1055 Very heavy corrosion. None (control) 40. 0203 0. 0 41. 4173 1. 3070 Do.

1 Surface area.

EXAMPLE 3 The process of applying the resin vehicle to the metallic substrate consists of applying the aforementioned vehicle with dispersed resin to the substrate by dipping, spraying or brushing. Following the application step, the coating is cured by evaporating off the volatile solvent.

Generally, the metallic substrate will be adequately protected when it has a high molecular weight polysulfone resin coated on its surface in an amount of from 0.05 to 25 grams per square foot of surface. This is true whether or not the resin is bonded directly to the metal surface or to an intermediate layer of paint. Alternatively, the amount of resin coating needed to protect the metallic surface may be expressed as 03-40 weight percent based on the metallic substrate.

For purposes of specifically illustrating, without limiting the invention, the following didactic examples are presented. All parts and percentages are to be taken by weight unless indicated to the contrary.

EXAMPLE 1 In an experiment to observe the effect of salt water on a C -C int-olefin polysulfone treated steel plates, the data in Table I was obtained (static test).

Five hard steel (ASTM Type A285C) panels, 3 x 6" x were cleaned with steel wool, acetonerinsed, weighed, and coated by brushing on a 5% by It can be seen from the above data that the polysulfone coated panel had the least amount of AlCl deposited on its surface and yet it had the lowest weight of coating applied.

The data in Table III were obtained in an experiment to determine the acid-resisting qualities of a C C a-olefin polysulfone coating.

Four aluminum plates (3" x 6" x 50 mils thick of the type used in Example 2 were cleaned with steel Wool, acetone rinsed, dried and weighed. The plates were then coated with various loadings of the C -C a-olefin polysulfone prepared by the process of the aforementioned application using a 1" paint brush and a 5 percent by weight toluene solution of the polysulfone.

One liter of 5 N HCl was placed in a 2 liter beaker at 53 C. The plates were placed upright around the side of the beaker and removed after five minutes. The plates were water washed immediatelyacetone rinsed, air dried, and reweighed.

TABLE III.ACID-RESISTANT PROPERTIES OF POLY- SULFONE COATINGS weight perchloroethylene solution of the coating ma- Ori ml r l t W558: Wm); p ig terials including the high ngolzcula; wmghbpolgsulfoi e 0 PF P( 3 2 g 5 5, 2 g/ 1? Thickre ared b the rocess o t e a orementione a 1- 0 n g-3 in. min. test (it. 1 ness, ati on The films wsere cured for hours at 20 C. a nd plate Surface area) N Hcl 901mm) 1115 h anels were 0.0 32.8850 6.6108 0 40 65% relat ve humidity and re weighed lT e p l h h M227 361618 4.0652 5,000 placed upright around the walls of a ga lon bott e w 1c M549 37,2473 29638 21070 48 contained a 4.76 percent by weight solution of sodium 0.1035 40.0250 0.2670 1,100 50 chloride in distilled water. The solution was kept sealed at 23 C. for days, after which the panels were removed, washed free of corrosion with deionized water,

and visually graded as to condition.

TABLE I.CORROSION STUDY OF POLYSULFONEzCOATED STEEL IN SALT WATER Wt. of plate Plate wt. Wt. of after 130 lost after Condition of plate Initial plate coating days in salt 130 day after 130 days in salt Coating applied weight (g.) (g./36 in?) water (g.) (g.) water lt'iidex 80-100 149.7484 0.0510 148. 0173 0.8821 Very heavy corrosion.

lfii ailiii wgi 151. 4177 0. 0294 151. 1300 0.3171 Heavy corrosion. C C 0z-olefi11polysulfone. 148.9060 073% S/lighti corrosion.

3 149. 5685 .02 ei'y ieavy corrosion.

1 H692 511mm 140. 2010 0.0 148.8400 0. 4210 Do.

None (control) 1 Surface area. 2 Melting point F. I 3 A silicone from the Pittsburgh Plate Glass Corporation.

It can be seen from the above data that the polysulfone-coated steel plate lost very little weight and ap- It can be seen from the above data that a low loading of polysulfone protected the aluminum plate from the peared significantly better than the other panels present. 75 acid.

EXAMPLE 4 Aluminum and steel panels, 3" x 16" x were cleared with steel wool, acetone rinsed, dried and weighed. The panels were then coated with the same polysulfone solutions used in Example 3 using a 1" paint brush. After drying the panels were weighed and painted with a commercial paint, Glidden Companys Speed Enamel #455, Outside Industrial Enamel containing 28.4% Pigment and 71.6% Vehicle.

The paint was observed to flow on the panel very smoothly and easily with few fish eyes visible. From the data in Table IV is can be seen that the polysulfone can be applied as an undercoat or overcoat for metal.

Table VI-- x 6" unground steel Q-panels, type R-36,

mill finish (Q-Panel Co., Cleveland, Ohio).

Table VIIA285C, a commercial hard steel.

Table VIII-A commercial grade of mild steel.

All panels in Table VII, Table VIII and panels #16, 18, #19 and #23 of Table VI were cleaned by dipping in 25% HCl containing 0.3% (vol.) of an abietic amine TABLE IV.-PAINTING QUALITIES OF METAL COATED WITH POLYSULFONES Wt. of panel Wt. of Wt. of Initial panel plus polymer polymer coating Wt. of painted paint applied Metal weight (g.) (g.) (g./36 in?) 1 panel (g.) (g./36 111. 1 Coating sequence Aluminum 40. 3123 0. 41. 0400 0.7277 Paint only.

39. 9837 40. 7112 0. 0201 40. 6911 0. 7074 Paint; then polysulfone overcoated. 40. 3718 40. 4273 0. 0555 0. 0 Polysulfone only. 40. 2874 40. 3225 0. 0351 41. 2655 0. 9430 Polysulfone undercoat; paint overcoat. 40. 1683 40. 2216 0.0532 41. 1334 0. 9119 Do. 146. 4733 0.0 147. 2534 0. 7801 Paint only. 145. 9969 146. 7309 0. 0901 146.6408 0. 6439 Paint undercoat; polysulfone overcoat. 149. 0158 149. 6426 0. 0268 149. 6158 0. 6000 Do. 149. 6417 149. 6907 0. 0490 0. 0 Polysulfone only. 149.6952 149. 7249 0. 0297 150. 4821 0.7572 Polysulfone undercoat; paint overcoat. 149. 7030 149. 7584 0. 0545 150. 6300 0. 8716 Do.

1 Surface area.

EXAMPLE The data in Table V was obtained (Accelerated Test) in an experiment to see if C C u-olefin polysulfones would protect steel panels in deionized water.

Seven steel panels, 3" x 6", Type S-36, 0.032 inch thick Cold Rolled Steel, Ground Q-Panels (Q-Panel Co., Cleveland, Ohio) were coated with a 5 percent by weight mineral spirit solution of the polysulfone of Example 1. Three other panels served as controls. The panels were then submerged 3" in a Precision Scientific Co. stirred water bath (Model #66648) maintained at 90 F. 2. The bath allowed a constant flow of 0.1 gallon per hour of deionized water to enter and to leave the system. The upper 3" of the metal panel was left explosed to normal laboratory atmosphere.

type inhibitor (Dowell A74 HCl acid inhibitor, Dow -Industrial Service, Cleveland, Ohio) for a period of 30 minutes. The panels were then water washed, acetone rinsed, over-dried for 2 hours at 90 C., cooled, weighed and then coated with 5 percent by weight of mineral spirit solutions of the various waxes and polysulfones.

After coating, the panels were air-cured (20 hours at 23 C., relative humidity), reweighed, and placed on an open laboratory roof, exposed on all sides to a chemical plant atmosphere. The panels were placed 3" apart in an upright position, treated portion upward, on a panel rack which allowed the panels to face in a eastwest direction. The panels were observed every five days Method of Wt. of

Appearance of panel after 110 days in test a o in ane in.

P nel c at g p g 1 Air exposed half Submerged half Polysullone; 1 coat Dipped 0 0948 Perfect A few rust spots. Polysulione, 2 coat-.. do .l .1644 do Do. Polysultone, 2 coat... Brushed 0 1565 do Do. Polysulfone; 1 coat-.- ..do 0.0937 do Do. Solvent treated Dipped 0 0000 Very heavy corrosion Very heavy corrosion Control-no treatment .0000 do o. Polysulfone; 1 coat Dipped 0 0201 A few rust spots visible. A few rust spots. Polysulfone; 1 coat do 0.0032 Light corrosion Do. PPG Multi prime coat 2 d0 0. 8309 Perfect Bubbles in coating. polysulfone; 1 coat untreated ...do 0.0496 Treated-perfect; untrcatedheavy corrosion Treated-a few rust 1 Surface area.

spots; untreatedheavy corrosion.

2 PPG Multiprime UC8171A commercial lead oxide metal primer from the Pittsburgh Plate Glass Corp.

It can be seen from the data above that light coatings of polysulfones protect metals from corrosion over extended periods of time.

EXAMPLE 6 An experiment was conducted to compare anti-corrosion properties of high molecular weight C -C alphaand their condition noted, numerical order being maintained at all times.

Durin the test period, weather conditions varied greatly: Temperature-lows of 38 F. and highs of were recorded; days of sunshine, rain, fog and high humidity were also observed.

TABLE VI.-CORROSION STUDIES OF COATED STEEL Q-PANELS EXPOSED TO CHEMICAL ATMOSPHERE Coating application Area rate Coating coated (ftfi/lb. Initial condition Condition of panel after Coating applied wt. (g.) (in?) coating) of coated panel 15 day test exposure" Panel No 1 Q-panel-as is 0. 000 21 Very heavy rusting.

2 Mineral spirits only (eontroi) 0.00 21 Do.

3.. Toluene only (control) (eommer 0.00 Do.

5 Texaco rust proof 1.20 Rust on edges only.

Paraifin wax 0. 038 Medium to heavy rusting.

0. 019 15 Do. 0. 023 21 Heavy rusting. 0.013 20 Heavy to very heavy rusting. 0. 068 21 Medium to heavy rusting. O. 050 21 D0. 0.035 18 Heavy rusting. 0.030 21 do Do. 0. 309 21 215 Holes visible No sign of corrosion. 0. 148 18 4 Very good Do. 0. 131 18 d Do. 0. 106 18 DO. 0. 088 18 Do. 0. 045 20 Very light rusting. 0. 048 23 Light rusting. O. 042 23 Busting on edges only. 0. 043 24 Medium rusting. 0.023 20 2,760 d0 Do. 0. 023 24 3, 282 Holes visible Medium to heavy rusting. 0. 023 24 3, 372 Very good Do. 0. 015 24 5. 010 Poor, many holes--. Heavy rusting. 0.010 24 7, 740 o Very heavy rusting. 0.007 20 8, 650 Poor, holes visible... Heavy to very heavy rusting. 0.004 19 15,000 do Do.

Definition of observations of panel conditions: Light rusting=Less than 30 (estimated) small, pinhead-size spots over entire coated portion of panel Medium rusting=Less than 200 (estimated) small (162) spots over entire coated portion of panel; Heavy rusting: Entire coated portion of panel covered with rust film; Very heavy rusting=Entire coated portion of panel covered with very heavy rust layers.

TABLE VII.CORROSION STUDIES OF COATED HARD STEEL PANELS EXPOSED TO CHEMICAL ATMOSPHERE Coating Area application Initial con- Coating coated rate (itJ/lh. condition at Condition of panel after Coating applied wt. (g.) (in!) coating) coated panel 15 day test exposure Panel No 1 Mineral spirits only (control) 0.001 8 ControL. Very heavy rusting. 2-- Paraffin wax 0. 019 S 1,330 o Light to medium rusting. 3.. 0.014 8 1, 858 do Medium rusting. 4 do 0. 009 8 2, 855 do Heavy rusting. 5.. Polyethylene wax. 0. 038 8 ..do Light rusting.

Oil-C20 polysulione 0.032 8 795 Very good.-. Do.

..... 0.017 8 1,480 do Mediumrusting.

Definition of observations of panel conditions: Light rusting=less than 30 (estimated) small, pinhead-size spots over entire coated portion of panel; Medium rusting=less than 200 (estimated) small Ofn) spots over entire coated portion of panel; Heavy rusting= entire coated portion of panel covered with rust film; Very heavy rnsting=Ent1re coated portion of panel covered with very heavy rust layers.

TABLE VIII.CORROSION STUDIES OF COATED MILD STEEL PANELS EXPOSED TO CHEMICAL ATMOSPHERE Coating Area application Initial con- Coating coated rate (itfl/ dition of Condition of panel after Coating applied wt. (g.) (111. lb. coating) coated panel 15 day test exposure Panel N o.:

1 Toluene only- 0.001 24 Control. Very heavy rusting. 2 Parafiin wax 0. 080 21 829 Very good Light to medium rusting. 3 do. 0.043 24 5 do Medium to heavy rusting. 4 do 0.022 24 Do.

. Polyethylene wax. 0. 101 20 Light to medium rusting.

Clo-C20 polysulione 0. 142 21 No sign of corrosion.

0. 048 24 Very light rusting. 0.040 24 Light rusting. 0.019 18 Medium rusting. 0. 020 21 0 D0. 0.018 21 3, 680 .do Do.

Definition of observations of panel conditions: Light rusting=Less than 30 (estimated) small, pinhead-size spots over entire coated portion of panel; Medium rusting=Less than 200 (estimated) small ($62") spots over entire coated portion of panel; Heavy rusting=Entire coated portion of panel covered with rust film; Very heavy rusting=Entire coated portion of panel covered with very heavy rust layers.

From the data given in Tables VI, VII and VIII it can be seen that C C a-olefin polysulfones are more effective anti-corrosion agents than are paraflin wax and low molecular weight polyethylene wax. It can also be seen that the polysulfones are more effective anti-corrosion agents at low application rates than polyethylene wax and paraffin wax are at much higher application rates.

I claim:

1. A corrosion resistant article of manufacture comprising:

(a) a normally corrosion-prone metallic substrate and (b) at least one coating thereon consisting of a high molecular weight polysulfone resin formed by the copolymerization of sulfur dioxide and a member of the group consisting of an alpha olefin of l20 carbon atoms and mixtures thereof and having a peak molecular weight in the range from 1.5 X 10 to 2.5 X

2. An article as defined in claim 1 in which the metallic substrate is selected from the group consisting of aluminum, zinc, lead, nickel, magnesium, iron, copper, alloys of the foregoing metals with each other and other metals.

3. An article as defined in claim 1 in which the resin is bonded on said metallic substrate.

4. An article as defined in claim 1 in which the resin 10 is bonded on said metallic substrate and is overcoated with paint.

5. An article as defined in claim 1 in which paint is bonded on said metallic substrate and is overcoated with the resin.

6. An article as defined in claim 1 in which the resin coating is present in an amount of about 0.05 to about 25 grams per square foot of metallic substrate.

7. An article as defined in claim 1 in which the polysulfone resin is an interpolymer of sulfur dioxide and an alpha-olefin of 10 to 20 carbon atoms.

References Cited UNITED STATES PATENTS 2,201,554 5/1940 Marvel et al 26079.3 2,474,350 6/ 1949 Eilerman 260-793 2,958,611 11/1960 Ulrich 11775 WILLIAM D. MARTIN, Primary Examiner R. HUSACK, Assistant Examiner U.S. Cl. X.R. 

